Semiconductor devices such as power semiconductor modules and various other parts are used in power conversion systems, such as inverters and converters, and in on-board electrical circuits. These semiconductor devices and various parts are often exposed to vibration environments during their operations.
Next is described a mounting structure for a printed circuit board, in which a printed circuit board having a heavy material such as a transformer, a capacitor or other electrical circuit part thereon is mounted on a chassis (a housing) fixed with a power semiconductor module or the engine of an automobile. An object (the power semiconductor module or the automobile chassis) onto which the printed circuit board is mounted is referred to as “main body” herein.
FIG. 7 is a cross-sectional diagram showing substantial parts of a conventional printed circuit board mounting structure. Fixation members 2 are fixed to corners of a main body 1, and a printed circuit board 5 is disposed above the main body 1 in such a manner that corners of the printed circuit board 5 are positioned on the fixation members 2. The printed circuit board 5 is fixed to the fixation members 2 by screwing the corners of the printed circuit board 5 with screws 10.
However, when the printed circuit board 5 is larger than the main body 1, the screws 10 are placed not only on the corners of the printed circuit board 5 but also on the other parts of the printed circuit board 5 at predetermined intervals.
A heavy material 3, such as a transformer, a capacitor, or an inductor, is fixed in the central part of the printed circuit board 5. Light materials 4, such as resistors or semiconductor elements, are fixed around the heavy material 3. In other words, the heavy material 3 and the light materials 4 here are electrical parts.
This conventional mounting structure for the printed circuit board 5 in which the corners of the printed circuit board 5 are fixed by the screws 10 and the fixation members 2 is a beam model structure for supporting both ends of the printed circuit board 5. Therefore, when the main body 1 vibrates, the printed circuit board 5 consequently vibrates. The printed circuit board 5 vibrates with large amplitude with low resonance frequency because the printed circuit board 5 has the heavy material 3 fixed at its central part.
An electronic circuit device described in Patent Document 1 has a lower substrate on which a principal circuit is formed, an upper substrate on which a drive control circuit for controlling drive of the principal circuit is formed, and a resin case. This resin case has external lead terminals of the principal circuit and the drive control circuit at an external surface of a circumferential edge and has a substrate storage space on the inside of the circumferential edge. In this electronic circuit device, the upper substrate is located above the lower substrate, and the space above the lower substrate is filled with filler. In this electronic circuit device, resin is used as the filler, and a supporting material is fixed to a position above the lower substrate with the hardened resin. Fixing and supporting the upper substrate using this supporting material can enhance vibration resistance and reliability of the upper substrate. For example, four of the supporting materials (such as bolts) are disposed around a heavy material to fix the heavy material onto the upper substrate.
Patent Document 2 describes a power semiconductor device in which a power element is sealed into a package. This semiconductor device contains the package, the power element fixed into the package, bonding wires connected to the power element, and a gelled insulator covering the power element. The inside of the package is filled with a foaming material so as to fill a hollow section remaining in the package. This can prevent damage due to resonance of the components of the power semiconductor device which is caused when the power semiconductor device is used under conditions in which vibrations are applied thereto from the outside.
Patent Document 1: Japanese Patent Application Publication No. 2008-166358
Patent Document 2: Japanese Patent Application Publication No. 2003-68940